Protected storage is required for many agricultural commodities, such as cereal grains (wheat, corn, or rice), pulses, oilseeds, dried fruits, nuts, cocoa, coffee, and spices, as well as seeds for the above, partially processed food such as flours, semolina, and others, and feed. Such commodities must be protected from the direct and indirect effects of oxygen and/or an increase in moisture, each of which permits growth of insects and/or microorganisms.
It is recognized that when commodities are harvested, there is a high likelihood that insects may be present along with the harvested commodity. If left untreated, the insect population may undergo rapid growth, resulting in damage or contamination of the commodity.
One approach to prevent losses from insect infestation is to use contact pesticides, or fumigants, and to prevent fungi development by the use of chemical preservatives on the commodity during storage immediately after harvest or prior to shipping. The use of these pesticides and chemicals is undesirable, as many pesticides can have an adverse effect on the health of the user, the consumer or the environment, including earth's upper atmosphere, and further may cause the development of insect resistance to the pesticide.
Other solutions to the infestation problem include refrigeration or the use of large flexible, hermetically sealed enclosures during storage, referred to as Cocoons™ (GrainPro, Inc. Concord, Mass., USA). In some cases, vacuum is added for more rapid disinfestation, such as is described in U.S. Pat. No. 6,609,354 to Villers and U.S. Pat. No. 6,941,727 to Villers, all of which are incorporated by reference herein in their entireties.
Specifically, a bulk commodity is hermetically sealed in a flexible container or enclosure, such as that formed from a 0.032 inch, low gas-permeability, UV resistant food grade PVC sheet material. A vacuum is established in the enclosure by using a conventional commercial vacuum pump and set point regulator. The flexible container or enclosure prevents excessive stresses when evacuated as would occur with a rigid container by conforming to the shape of the enclosed commodity. An opening, which can be opened or closed by means such as a solenoid-controlled inlet valve, is fed to an ordinary vacuum pump, with, if needed, an appropriate filter at the hermetically sealed container end to prevent clogging or damage to the pump. The vacuum pump is allowed to run for an extended period of time so that either or both Oxygen and interstitial moisture inside are substantially removed, typically down to a vacuum of 25-100 mm Hg at room temperature representing a level equivalent to, at atmospheric pressure, 0.7-2.75% oxygen. At this time the valve is closed, and the hermetically sealed container becomes a large “vacuum pack,” with periodic pumping as required to compensate for residual infiltration of air, eliminating any of the respective causes of degradation named above due either to direct or indirect effects of Oxygen. Further, any residual moisture in the absence of Oxygen will not as easily cause moisture-produced damage. Damage to the commodity can be prevented, at least in part, by restricting the metabolic activity of all biological agents, including insects, microflora, and the commodity itself.
In a particular implementation, a vacuum in the range of 25-100 mm Hg is established in the enclosure at 20° C. or higher. The appropriate minimum temperature is based on the particular infesting biological contaminant(s) and the desired kill time of the biological contaminant(s). The commodity can have a weight in the range of one-half to two hundred metric tons.
However, the Cocoons™ are restricted by the requirement that they be sufficiently hermetic to allow a low oxygen atmosphere to develop due to insect and/or commodity respiration and to prevent significant moisture ingress in humid atmospheres. The use of large bags provides more volume/surface area and as such, lowers permeability per ton. Thus, the smallest feasible Cocoons™ are limited by permeability considerations of available robust and moderately priced materials to a minimum capacity of about 7.5 cubic meters in bags with approximate dimensions of 2 m×3 m×1.5 m. Alternatively, flexible enclosures may be constructed somewhat smaller with a minimum volume of 0.7 m3, such as the product GrainSafes™ (GrainPro, Inc. Concord, Mass., USA), as described more fully in Israeli Patent Number 122456, incorporated herein by reference in its entirety. However, this size involves compromises in the degree of permeability and therefore the ability to kill insects based on their, and the commodity's, respiration rates versus infiltration rates of oxygen from the outside. Thus, these enclosures are too large and too unstable to be readily transportable when full.
Bags which are easily human-portable are generally comprised of (high permeability) jute or woven polypropylene bags, and are typically in the 25 to 100 kg capacity. Machine transportable bags, known as “Big Bags,” are generally in the 500 to 1000 kg capacity. Although flexible, such bags alone do not afford sufficient protection from infestation or molds, do not result in a low oxygen atmosphere, or prevent the effects of absorbing moisture from the atmosphere.
The material used for the Cocoons™ described above is a food grade flexible PVC plastic typically 0.83 mm thick, sold commercially by GrainPro under the trade name of Cocoon™ and for the smaller container, GrainSafe™. This PVC material is not suitable for long-term storage of small quantities; it is relatively too permeable, expensive and too stiff to be used in individual bags below five ton size without significantly compromising performance. Alternatively, semi-rigid aluminum bags, commonly known as “Joseph” bags, have long been available, and are comprised of relatively rigid aluminum coated plastic. These “Joseph” bags, however, are expensive, easily punctured, difficult to close, and do not protect against insect penetration, making them a less than optimal choice. Other forms of hermetic enclosure include amphores (large earthenware containers) as used in ancient times, lined underground pits sealed with a variety of substances, and metal or plastic drums. None are lightweight, flexible, inexpensive and easily transportable.